Documentation?

> Is there equivalent functionality with Xft? And whose responsibility it
> is now, if this functionality is not here: applications, toolkits or
> something else?
Xft provides the DPI information, the desktop permits the DPI to be
configured providing some muppet hasn't decided that is too complicated
and taken it away from you.
From memory Gtk and Qt use Xft values if available and the server reported
DPI for the display if not.
In the perfect world the monitor would report the DPI reliably to the
Xserver which would adopt it and everything would just work.
Unfortunately monitors report rather varied things, the dominant OS
product appears to ignore the monitor value entirely (so the monitor
doesn't get corrected) and everyone forces an OS dependant DPI in their
desktop ignoring all the monitor info.
Wile for most purposes the end result of that entire process is "96"
Pango and friends deal in points so can provide what you want.
Alan